Bitument impregnated fiberboard



April 30, 1963 H. w. BEuscHER Erm. 3,087,851

BITUMEN IMPM-:ammoy FIBERBOARD Filed Jan. 26, 1961 United States Patent O 3,087,851 BITUMEN IMPREGNATED FBERBOARD Howard W. Beuscher, Dubuque, Iowa, and John I. Geary,

Lewisburg, and Dorsey J. Morris, Middleburg, Pa., as-

signors to Allied Chemical Corporation, New Yom,

N.Y., a corporation of New York Filed lan. 26, 1961, Ser. No. 85,138 6 Claims. (Cl. 162-171) This invention relates to iiberboard, and more particularly refers to a new, .improved process for production of bitumen impregnated liberboard and to improved products produced therefrom.

Fiberboard products are conventionally produced by the Iformation and process-ing of aqueous slurries of fibrous material. yExamples of the many iberboard products in use today include sheathing, interior board, ceiling tile, chipboard, insulating board, hacker board, form board, core board, oor underlayment board, cantstrip, and the like. Fiber-board may be generally divided in two classes-tiberboard in which no or small amounts of coating asphalt is incorporated and berboard in which asphalt is distributed throughout the body of the board. This latter type liberboard designated asphalt impregnated liberboard has particular application in construction and is to be distinguished ctrom iiberboar-d containing no asphalt and from liberboard which has only its surface coated with asphalt. Examples of such impregnated fiberboard products `are nail-base sheathing to which an exterior iinish can be directly nailed, insulating sheathing, and structural ysheathing particularly for use where no corner-bracing is required. Sheathing materials of these types are used in home building and about 900,060,000 square feet are .currently used annually in the United States. Sheathings of these types contain about -'35 percent by weight asphalt which influences such important characteristics of the board as nail-holding ability and dimensional stability as well as Warpa-ge, weather resistance and lateral strength. Asphalt impregnated sheath- -ing products are conventionally produced by dispersing the bituminous material in the aqueous slurry of bers which is then passed to the board-forming machine and dewatered to form a ibrous mat or wet lap which is then dried to produce the liberboard.

A problem of long standing in the production of asphalt impregnated berboar-d has been in the use and introduction of the bituminous binder which must be thoroughly admixed in the fibrous stock before the board-forming operation to produce a satisfactory product. As bituminous materials are basically incompatible with the large amounts of water contained in the fibrous slurry being processed, it has been heretofore conventional to accomplish the introduction of the bituminous material in the form of a dry powder w-hich may be obtained commercially or by pulverizing larger size particles. While these methods produce a satisfactory product they are all subject to serious disadvantages and the industry has been forced to tolerate many vexing problems attendant in their use. When a dry powdered asphalt is used, the particle size may be extremely small and retention of the powdered binder in the librous mat during the board-forming operation is less than `desired with a significant portion of the powdered material contained in the water draining from the mat and ultimately discharged as waste. The extremep IC@ ly fine size of the asphalt powder also presents a serious dust problem in handling which is objectionable to operating personnel and severe enough to constitute an explosion hazard in confined spaces. Further, the use of bituminous material in powdered form has required the use of a material having a relatively high softening point which tends to cause resistance to flow by heat in the dryer thereby retarding good and uniform bonding of the fibers by the bituminous material. As a result, sheathing products produced trom powdered asphalts have only minimum or border line dimensional stability which would tend to make the boar-d more likely to buckle or warp. The use of a pulverized asphaltic material is subject to disadvantages of processing explosion and handling hazards, high installation and processing costs, and variation in particle size over a wide range which is detrimental from a product standpoint. Metering of required amounts of the pulverized asphalt is extremely diicult because of its incompatibility with water.

In a limited number of cases the bituminous binder is also introduced in the form of an emulsion. In addition to required expensive emulsifying agents and procedures, the use of asphalt emulsions results in the introduction of particularly tine particles which are also subject to loss in large quantities in waste from the process. As a result, the use of asphalt emulsions has been narrowly limited to the production of low-asphalt content liber-board .containing usually less than about 2. percent asphalt by weight. Attempts to use an asphalt emulsion in the production of higher asphalt-containing sheathing products not only results in the loss of a large amount of the asphalt but also requires the use of large amounts of expensive chemical agents to free the material from the emulsion.

The art, as illustrated by U.S.'P. 2,036,466, found impractical Ithe use orf liquid asphalt and required the introduction of powdered -asphalt Afor use in the production of asphalt impregnated iiberboard notwithstanding the numerous indicated disadvantages. The art has given much attention to the `development of improved methods including the introduction of a liquid bituminous material but without success. In our own experimentation we have tried a number of 4methods of introducing liquid asphalt into the stock and `confirmed the prior art failures in that they resulted in agglomeration of the liquid bituminous material in the stock causing an almost immediate clogging of the system and shutdown of the process.

An object of the present invention is to provide an improved method for producing bitumen impregnated tiberboard by incorporating molten bitumen into the aqueous slurry of fibrous material. Another object is to provide a method for producing asphalt impregnated berboard having improved dimensional stability and greater nail-holding power.

A further object of the present invention is to provide a method for producing asphalt impregnated iberboard utilizing lower softening point asphalt.

Other objects and advantages will be apparent from the following description and accompanying drawing.

In accordance with the present invention we have ifound that asphalt impregnated iiberboard having improved properties can be produced without the use of powdered or pulverized asphalt with their attendant disadvantages lby forming a stock comprising a slurry of fibers suspended enst/,asl

in water, generally about l-lO percent by Weight fibers in the slurry, as is conventional in the art, introducing normally solid asphalt having a softening point within the range of l40260 F., preferably within the range of l50l95 F., in molten condition, preferably at a temperature between 250-600 F., desirably at a temperature of about 300-500 F., in the form of a fine stream into a flowing stream of aqueous slurry at a temperature below the softeningy point of said asphalt to cause solidification of the molten asphalt on contact with the flowing stream of -aqueous slurry and rapidly removing the solidified particles of asphalt lfrom the Zone of introduction of the asphalt by the fiowing stream of aqueous slurry. Liquid asphalt introduced in accordance with the invention in molten form becomes dispersed in the stock in the form of solidfied asphalt particles formed on contact of the molten bituminous material with the cooler body `of stock. The solidified asphalt particles so formed are brittle or crumbly in nature and can, if desired, be readily broken down by simple refining to more discrete particles prior to sending the stock to the boardforming machine.

The use of liquid molten asphalt as compared to powdered asphalt in the production of asphalt impregnated fiberboard has several distinct advantages. The loss of asphalt material in the process is materially reduced and also smaller amounts of asphalt are required within the fibrous mat as compared with the powdered form. Of particular importance is the ability `of the process of the present invention to utilize a lower softening point asphalt within the range of l40-195 F. which results in a fiberboard product having superior properties, particularly dimensional stability and nail-holding properties, over that using powdered asphalt. Powdered asphalts are of necessity limited to asphalts having a softening point well in excess of 200 F., generally about 230-300 F. or more, for the reason that lower softening point asphalts do not lend themselves to grinding because the heat generated during grinding causes fusion of the particles. In the production of fiberboards, the wet fiberboard passes through a dryer for the purpose of removing moisture. The temperatrue of the board during the drying `operation rarely exceeds 230 F.mueh higher temperature might cause scorching and would be uneconomical. Consequently, the temperature of the board is near or below the softening point of the powdered asphalt with little or no flow of the asphalt and incomplete impregnation and bonding of the fibers. As a result it has been difficult to produce asphalt impregnated fiberboard having minimum properties and in fact to partially compensate for this lack of fiowability appreciably larger quantities of asphalt have been required. In the process of the present invention wherein molten asphalt is employed expensive grinding and pulverization is eliminated which markedly reduces the cost of operation. Also in accordance with the present invention a lower softening point asphalt, between about l40l95 F., may be utilized, which asphalt dispersed in the board when subjected to the drying operation readily ows and impregnates and bonds the fibers much more effectively than the higher softening point powdered asphalt to produce a superior product which has greater dimensional stability and better nailholding properties. It has also been found that less asphalt is required.

The invention will be more readily understood and described in detail by reference to the accompanying drawing which illustrates diagrammatically a typical process for the production of asphalt impregnated cellulosic fiber board and shows in detail a preferred embodiment of the invention indicating location and method for introducing liquid asphalt employing a spreader plate for directing a film of molten asphalt into an overflowing aqueous stream containing asphalt and cellulosic fibers.

The process outlined by the accompanying drawing is merely illustrative and many variations not mentioned below may exist in actual practice regarding materials employed, the introduction of these materials, control of the process, and the use, type and arrangement of equipment.

Referring to the drawing, cellulosic raw material, typically in the form of wood chips, is withdrawn from storage silo 1 and conveyed 'oy bucket elevators 2 through line 3 to digester hopper 4. The cellulosic raw material employed may lbe any of several types including hardwood chips of woods such as oak, maple, birch, aspen, poplar, linden, etc.; and the softwoods such as pine and hemlock. In addition, other materials auch as fiax, cereal straw, corn stalks, sugar cane, licorice roots, etc. or essentially any material including mineral substances such as asbestos which can be reduced to a fibrous pulp may also be used for making asphalt impregnated fiberboard products. In some plants paper and rags are also added. In general, the specific raw materials depend on many factors including availability, cost and the specifications of the final product. Commonly, two or more fibrous materials will be blended.

From hopper 4 the wood chips are fed by feed screw conveyor 5 into one end of digester 6. Screw conveyor 5 exerts a compressive action on the chips to form a high density plug enabling pressure to be maintained in digester 6. In the digester the chips are admixed with a softening agent introduced through line 7, and subjected to the action of steam from line 9 and pressure while being conveyed the length of the digester by means of a timing screw 3 which can be varied in speed to regulate retention time. From digester 6 the treated cellulosic material is forced by steam through discharge valve 161 operated by discharger 11 and then through blow line 12 to cyclone collector 13. Material discharged from digester 6 is in the form of coarse cellulosic fibers which need further refining to be suitable for board manufacture. rl'he coarse fibers are worked through the bottom of cyclone collector 13 to conveyor 15 and delivered through line 16 into primary refiner 17. Primary refiner 17 is driven by motors 18 and has revolving metal discs which grind the coarse fiber to more discrete fibers or pulp. A small amount of water at a temperature of about 1502160" F. is delivered to line 16 and facilitates the passage of the fibers through the primary refiner 17.

The pulp discharged from primary refiner 17 is admixed with large amounts of water entering through line 19 at a temperature of about F. to about 140 F., to form an aqueous slurry of cellulosic fibers. A portion of the water entering through line 19 has been recycled in process and enters line 19 from line 20. The resulting slurry then flows by gravity through fiume 22 to refiner chest 23 which serves as a temporary retaining vessel or surge tank under constant agitation to retain the fibers in a slurried condition. From chest 23 the fibrous slurry flows by action of pump 24 through line 25 to thickener 26 where a portion of the Water is removed. Water removed from the slurry exits thickener 26 through line 27 from which a portion, typically 50-95 percent, is recycled through line 20 with the remainder passing to waste through line 27. The thickened slurry, at a consistency of typically about 4-10 percent and temperature of about 13052- F., is allowed to flow through line 28 to an agitated pulp chest 29, In thickener 26 it is conventional to remove a somewhat greater proportion of water than required to enable the slurry to be thereafter easily adjusted to the desired consistency by the addition of water. The thickened slurry is withdrawn from chest 29 and flows by the action of pump 30 through line 31 which discharges in the central section of blend consistency regulator 32 from which a controlled amount of the slurry 1of accepted consistency regulated by the addition of water through line 33, as desired, is allowed to advance in the process and exits regulator 32 through line 34. The remaining portion of the slurry overows a weir 35 in regulator 32 and is recycled by gravity flow through line 36 to storage chest 29; The fibrous slurry exiting regulator 32 through line 34 flows by gravity into an upper portion of the vortex-shaped blend box 35 and downwardly through line 39 while admixing with other fibrous slurries which have been separately processed in systems duplicating that described above. The various slurries entering blend box 38 may be of the same or different materials depending on the specifications of the fiberboard being produced. The resulting slurry entering machine chest 40 contains -typically 2 to 5 percent fibers and 98 to 95 percent water by weight, more generally about 3 to 4 percent fibers and 97 to 96 percent water. In blend box 38 chemical additives such as wax, rosin, etc. for sizing or other purposes may also be admixed as desired or required.

Machine chest 40 is maintained under constant agitation to ensure good mixing and maintain slurried condition. The slurry is withdrawn from machine chest 40 vand flows by the action of pump l42 through line 43 and is discharged in the central section `of machine consistency regulator 44. Consistency regulator 44 is similar in construction to regulator 32 and has a central section from which the stock iiows under one or more gates to an outer channel which encircles a major portion of regulator 44. Consistency of the stock is measured by pressure drop as the stock flows in the channel to va gate 45 through which a controlled amount of stock of suitable consistency regulated by the addition of water through line 46, as desired, is allowed to` advance in the process and exits regulator 44 through line 47. Stock in the outer channel not exiting the regulator is -allowed to overflow a Weir (not shown) into compartment 43. The remaining portion of the slurry entering regulator 44 overflows a weir 49 located in the central section into compartment 48 for recycling to machine chest 40. lt has been found that the -stream of stock overflowing weir 49 is satisfactory for the introduction of liquid -asphalt in accordance with the invention. Accordingly molten asphalt, desirably asphalt heated to a temperature abo-ve about 300 F., is withdrawn from tank 51 by pump 53 through line 52 and flow control valve 55 and introduced into the downowing stream overflowing weir 49 in the form of a fine stream of molten asphalt. Molten asphalt is recinculated to tank 51 through loop line 57. On contact with the colder aqueous stream the asphalt so introduced becomes dispersed therein and is carried away from the zone of introduction without agglomeration in the form of brittle, crumbly, solidied asphalt particles. The rate of introduction of molten asphalt may be varied over a wide range, being typically introduced at a rate to provide -30 percent, usually 15-20 percent asphalt by weight of total solids in the slurry when the process is directed to produce asphalt impregnated sheathing. In the procedure found to give best results the molten asphalt is introduced into the stock stream overflowing Weir 49 in the form of fine film. This may be accomplished by directing a stream of molten asphalt at a suitablel angle, typically 30-40, against a spreader plate 54 in such a manner that the resulting film enters the downflowing stock overflowing weir 49 into compartment 43, substantially as shown. The asphalt then introduced is carried away from the Zone of introduction in the form of solidified particl which disperse in the slurry of fibers in water, the resulting slurry exiting compartment 48- of regulator 44 by gravity iiow through line 56 to machine chest 40 for admixture with the stock entering chest 40 from blend box 3S.

The slurry exiting -machine consistency regulator 44 through line 47 contains the desired proportion of fibrous material to asphalt and flows by gravity to a secondary refiner 59 which is driven by motor 60. Consistency of the stock entering secondary reiiner 59 is typically 2.5 to 4.5 percent, generally about 3.0 to 3.5 percent. Retiner 59 has a revolving metal disc which further refines the fibers. Asphalt particles not already broken down or sufficiently small are also acted upon in refiner 59. The refined stock discharged from secondary refiner 59 through line 62 is usually given a final consistency adjustment by the addition of Water and deaerated by vacuum equipment (not shown) before entering head box 63 from which the stock is passed through line 64 to board forming machine 65. The stock at this point contains typically 1.5 to 4.0 percent, generally about 2.0-3.0 percent by weight fibrous material, 10430 percent, usually 15-20 percent asphalt based yon the iibrous material, and 1-5 percent by weight chemical additives based on the fibrous material and enters the board forming machine at a temperature of about -l35 F., preferably at a temperature of -130 F. Board forming machine 65 may be any of several types, for example, a moving Fourdrinier wire or screen on which a controlled amount of stock is distributed across its formation width. Water drains from the stock through the wire, forming a fibrous mat from which additional water is removed as the mat moves through the suction and press sections of the machine. The formed mat from the press section is then separated from the wire, cut into appropriate Working lengths, and passed to the dryer section in which substantially all of the remaining Water is removed in stages. Temperature of the board usually does not exceed about 230 F. during the drying operation in which the asphalt is softened to form a strong bond between the fibers in the finished product which exits the dryer section ready for trimming and fabrication.

Although the molten asphalt is preferably introduced into regulator 44, alternatively the molten asphalt may be directed into other rapidly flowing streams of stock in the process as for example into the stock downiiowing into blend box 38. Stock entering blend box 38 through line 34 flows downwardly through blend box 38 at a rate of about l0-14 feet per second and carries the asphalt so dispersed through line 39 into machine chest 40 in the form of dispersed solidified asphalt particles. The stock in machine chest -40 is admixed with the incoming stock and the resulting slurry passed by pump 42 through line 43 to the machine consistency regulator 44 and then processed as previously described except that the addition of molten asphalt in regulator 44 is omitted. Best results are obtained by introducing the molten asphalt into the d'ownflowing stock stream in blend box 3S in the form of a ne film. This may be accomplished -by positioning a spreader plate approximately adjacent the point of introduction in the blend box 3S of the stock stream entering through line 34. A stream of molten asphalt, desirably heated to a temperature above about 300 F., is then directed typically at an angle of 30-40 against the spreader plate with the resulting film entering the downflowing stock at an intermediate point in blend box 38. The asphalt so introduced is carried away from the zone of introduction by the downflowing stock in the form of essentially solidified particles formed on contact with the cooler body of downflowing stock which exits blend box 38 through line 39 and enters machine chest 40 where slurried conditions are maintained under agitation.

Conditions required for the introduction of la liquid bituminous bonding material in accordance with the invention are the use of a normally solid bituminous material in molten form, the introduction of the molten bituminous material in the form of a fine stream, and the introduction into a cooler flowing aqueous stream of stock to shock cool and form dispersed solid :asphalt particles in the stream with removal of the dispersed solid asphalt particles from the zone of introduction by the flowing stream of stock. When these conditions are satisfied, liquid bituminous material does not agglomerate on introduction but rather becomes dispersed in the aqueous stock in the form of solidified particles suitable for use and processing in the production of tiberboard. The

acer/,asl

stream of molten asphalt should have a iineness or thickness of less than about 1/2 inch, preferably less than about 3A; inch. The character of the fine stream of molten asphalt required for successful practice may be varied considerably and may take the form of one or more separate fine streams of limited thickness, a iine film, splash, spray, droplets, and the like. In every case a minimum iiow rate at least suflicient to remove the asphalt then introduced from the zone of introduction is required. In practice an aqueous stream of stock flowing at a rate of about 8-12 feet per second or higher has been found satisfactory although appreciably lower rates, say about 3 feet per second, may be employed dependent on the fineness and quantity of the asphalt. The molten asphalt may be introduced at various points in the process. For instance, the asphalt may be introduced into a blend consistency regulator in the same manner as indicated for the machine consistency regulator or into the aqueous body of stock downliowing in the pipe leading from a thickener to the stock chests. The molten asphalt stream may also be introduced into any aqueous body owing at a sufficient rate in the process but it has been found desirable to select a location where the stock has a consistency of about 1.5 or more percent to avoid the tendency of the asphalt particles to settle. When introduced after the thickener and into stock having a consistency of 1.5 or more percent suspension may be readily maintained under normal conditions as required to maintain the fibrous material in a slurried condition. Introduction before the blend box may involve working with one or more aqueous stock streams which are to be blended in the blend box. Hence, introduction of the molten asphalt into the blend box or machine regulator also permits complete introduction into a single stock stream and better control of the process. The size of the solidified asphalt particles obtained also depends on the particular indicated conditions employed and varies primarily with the tineness of the stream of molten asphalt and to a somewhat lesser extent with the rate at which the stock is iiowing. As a general proposition the finer streams of molten asphalt and faster stock iiow rates produce the smaller particles. The size of the solidified particles may therefore be as large as about 0.60 inch or as small as 0.05 inch and smaller when a very fine stream of molten asphalt is used. Depending on the size of the liber being processed and the specifications of the iiberboard product it is generally desired to have asphalt particles sized within a particular range -in order to obtain maximum bonding effect in the final product. As a precautionary measure to make certain the particles are of the desired degree of neness, the stock containing the larger particles may be passed through a secondary reiiuer, as described above, or through other suitable apparatus which has a disintegrating action to break down the larger particles. In this manner the smaller particle sizes can be readily produced without the need of closely controlled conditions to ensure introduction of the finer streams of molten asphalt. As the solidiiied particles formed in accordance with the invention are brittle or crumbly in nature, breakdown of the larger particles can be easily effected and to some extent takes placeV during normal passage of the stock through the processing system. The presence in the stock of solidified particles previously formed does not affect the introduction of additional molten asphalt. The fibrous material in the slurry may be varied and slurries containing any celluosic fiber may be used, or blends thereof, and other material, such as asbestos fibers may be substituted in whole or in part.

Any normally solid bituminous material suitable for use as binder for the class of products known as asphalt impregnated fiberboard may be used in molten liquid form in the present invention. Bituminous materials of this type include residual asphalts from the distillation of petroleum, air-blown asphalts, solvent extracted and solvent precipitated petroleum fractions, coal tars, watergas tars, wood-tars, rosin pitches, pressure still pitches and the like. Temperatures at which the molten bituminous material is employed may be varied over a fairly wide range, minimum temperatures generally vary depending on the softening point of the particular material employed. Generally, a temperature of about 70 to F. above the softening point is desired to insure suiicient fluidity. Best results are obtained when using a bituminous material heated to a temperature above about 300 F. Preferred temperatures are within the range of about 350 F. to about 500 F. Softening point of the bituminous material used may also be varied over a wide range and may be as high as about 260 F. or as low as about F. As indicated, the present invention permits the use of a bituminous binder having a relatively low softening point compared to the higher softening point material required in the prior art practice using other methods of introducing the bituminous binder. Accordingly, in the present invention it is preferred to use a bituminous material having a softening point Within the range between about 140 F. to about F. to produce bitumen impregnated berboard containing 10 to 30 percent asphalt and having a significantly greater dimensional stability and improved nail-holding characteristics.

'Ihe following example illustrates the present invention.

The raw material, wood chips, is digested in a pressure digester to soften and partially break down the tibers. T he treated chips are discharged under pressure and are blown by steam from the digester to a cyclone collector. From the cyclone collector the wood chips are conveyed to a primary retiner wherein the softened wood chips are ground in the presence of a small amount of water by revolving metal discs. The resulting coarse cellulosic fibers pass to a fiume wherein water is introduced to form an aqueous slurry of stock having a consistency of about 1.0 to 1.5 percent and a temperature of about 125 F. The stock flows by gravity into an agitated refiner chest from which it is withdrawn and sent to a thickener where the stock is thickened to a consistency of about 5 percent with excess water discharged from the thickener. The thickened stock is directed to a blend consistency regulator wherein water is mixed with the stock to adjust the consistency to a desired level and about 40-80 percent of the stock entering the regulator is recycled by passing to storage chest and returning to the regulator. The remaining portion of the stock in the regulator having an adjusted consistency or about 3-5 percent passes through the gate opening in the outer channel of the regulator. At this point separately processed streams of primary refined fibers are admixed in a blend box and the combined slurry flows by gravity into a machine chest. The slurry is withdrawn from the machine chest and fed into the central section of a machine consistency regulator in which a portion of the stock underliows one or more gates from an outer channel from which it exits. The remaining portion of the stock in the regulator overliows into a compartment at the rate of about 600 g.p.m. in the form of a rapidly owing stream. A solvent precipitated bituminous material consisting of about 8.0 percent asphaltenes, 89.0 percent resins and about 3.0 percent saturated hydrocarbons and having a softening point of about 183 F. is heated in a tank and fed in molten form at the rate of about 8-10 gpm. and temperature of 450-500 F. against a spreader plate from which the molten asphalt is deflected in the form of a film having an average thickness less than about 1A inch into the downtiowing stock which has a temperature of about 115 F. The spreader plate is constructed of galvanized metal and is positioned a horizontal distance of about 12 inches from the weir and has a lower edge of 71/2 inches width situated at about 12 inches above the length edge of the weir. On contact of the film of molten asphalt with the cooler aqueous stream the asphalt becomes dispersed therein and carried away in the form of solidified asphalt particles which on examination were found to be brittle or crumbly in nature. The resulting slurry containing the asphalt particles flows by gravity to the machine chest and is recirculated to the regulator. Stock is withdrawn lfrom the regulator at a temperature of about 115 F. and fed under pressure to a secondary refiner in which the primary refined fibers pass through revolving metal discs and are further refined. Oversize asphalt particles in the stock are broken down to more discrete particles averaging approximately 80-200 mesh size. The refined stock is discharged from the refiner, additional water added to adjust the consistency to about 1.0 to 1.5 percent and the stock deaerated by Vacuum equipment. Resulting stock passes to a board-forming machine where the stock is distributed onto a moving Fourdrinier wire screen in the form of a mat. Water drains from the mat which latter is then passed over suction boxes and pressed by top-moving wire screen to remove additional water. The fibrous mat which is cohesive is separated from the moving screen and cut into 25-foot lengths for passage through the dryer section. Drying is by convection heating using circulating streams of hot air with the temperature of the board not exceeding about 250 F., generally not exceeding 230 F. Substantially all of the remaining water is removed in the drying operation and the final product has a water content of about 3 percent. The final asphalt impregnated fiberboard product has a thickness of about 1/2 inch.

Specimens lof the fiberboard product produced in accordance with the invention were tested for dimensional stability by the linear expansion test prescribed for insulating sheathing in A.S.T.M. D-'37 and in U.S. Department of Commerce Commercial Standard CS 42-49 and compared with the results obtained in identical tests on asphalt impregnated fiberboard produced from the same formulation using .a powdered bituminous asphalt having a softening point of about 230 F. Test results, summarized below indicate approximately a 30 .percent reduction in expansion or la significant improvement in product specifications in the use of the fluid asphalt system over the powdered asphalt system.

Linear expansion in Although certain preferred embodiments of the inv-ention have been disclosed for purpose of illustration, it will be evident that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

We claim:

1. lIn a process for the production of bitumen impregnated fiberboard .in which fibers are admixed with water to provide an aqueous slurry to which bitumen is added to form a stock comprising fibers and bitumen suspended in water and the stock passed to a board-forming machine to produce bitumen Aimpregnated fiberboard, the improvement which comprises introducing normally solid bitumen in molten condition in the form of a stream having a fineness of less than 1/z inch into a flowing stream of aqueous slurry moving at a rate of at least 3 feet per second and containing about 1-10% by weight fiber at a temperature below the softening point of said bitumen to cause solidification of the molten bitumen predominantly .in the form of frangible solidified particles on contact with the flowing stream of aqueous slurry and rapidly removing the frangible solidified particles of bitumen from the zone of introduction of the bitumen by the flowing stream of aqueous slurry.

2. In a process for the production of asphalt impregnated berboard in which fibers are admixed with water to provide an aqueous slurry to which asphalt is added to form a stock comprising fibers and asphalt suspended in water .and the stock passed to a board-forming machine to produce asphalt impregnated fiberboard, the improvement which comprises introducing normally solid asphalt having a softening point within the range of about 140- 260 F. in molten condition at a temperature between about 26o-600 F. in the form of a stream having a fineness of less than 3%; inch into la flowing stream of aqueous slurry moving at a rate of at least 8 feet per second and containing about 1-10% by Weight fibers in the slurry at a temperature below the softening point of said asphalt to cause solidification of the molten asphalt predominantly in the form of frangible solidified particles on contact with `the flowing stream of aqueous slurry and rapidly removing the frangible solidified particles of asphalt from the zone of introduction of the asphalt by the flowing stream of aqueous slurry, said asphalt being introduced in an amount to constitute about 535% by weight of the fibers and asphalt.

3. In .a process for the production of asphalt irnpregnated cellulosic fiberboard in which cellulosic fibers are admixed with water to provide an aqueous slur-ry to which asphalt is added to f=orm a `stock comprising cellulosic fibers and asphalt suspended in Water and the stock passed to a board-forming machine to produce asphalt impregnated cellulosic fiberboard, the improvement which comprises introducing normally solid asphalt having a softening point within the range of `about 15 0-195 F. in molten condition at :a temperature between about 300-500" F. in :the form of a stream having a fineness of less than 5%; inch into a flowing stream of yaqueous slurry moving at a rate of at least about 8 feet per second .and containing about 25% by weight cellulosic fibers in the slurry at a temperature below the softening point of said asphalt to cause solidification of the molten asphalt predominantly in the form .of frangible solidified particles on contact with the flowing stream of aqueous slurry and rapidly removing the frangible solidified particles of asphalt from the zone of introduction of the lasphalt by the flowing stream of `aqueous slurry, said asphalt being introduced in an -amount to constitute .about 10-30% by weight of the cellulosic fibers and asphalt.

4. In a process for the production of asphalt impregnated fiberboard in which fibers are admixed with water to provide an aqueous slurry to which asphalt is added to form .a lstock comprising fibers and asphalt suspended in water and the stock passed to a board-forming machine rto produce asphalt impregnated fiberboard, the improvement which comprises introducing normally solid asphalt having a softening point within the range of about 260 F. in molten condition at a temperature between about 260-600 F. in the form of a stream having a fineness of less than -1/2 inch into a flowing stream of aqueous slurry moving at a rate `of at least 3 feet per second and containing `about 1-10% by weight fibers in the slurry at a temperature below the softening point of said asphalt to cause solidification of the molten asphalt predominantly in the form of frangible solidified particles on contact with the flowing stream of .aqueous slurry and rapidly removing the frangible solidified particles of asphalt from the zone of introduction of the asphalt by the flowing stream of .aqueous slurry, said asphalt being introduced in an amount to constitute about 5-35% by weight of the fibers and asphalt, and subjecting the resultant slurry in which fibers and asphalt are -Suspended in Water to refining to reduce the fibers and solidified asphalt particles 12 range of 10-30% by Weight of the board and has a softening point Within the range of 150-195 F.

References Cited in the ile of this patent UNITED STATES PATENTS 1,877,377 Yungblut Sept. 13, 1932 2,035,921 Quinn Mar. 31, 1936 2,190,034 Levin Feb. 13, 1940 2,402,160 Heritage June 18, 1946 FOREIGN PATENTS 151,029 Great Britain Sept. 6, 1920 

1. IN A PROCESS FOR THE PRODUCTION OF BITUMEN IMPREGNATED FIBERBOARD IN WHICH FIBERS ARE ADMIXED WITH WATER TO PROVIDE AN AQUEOUS SLURRY TO WHICH BITUMEN ID ADDED TO FORM A STOCK COMPRISING FIBERS AND BITUMEN SUSPENDED IN WATER AND THE STOCK PASSED TO A BOARD-FORMING MACHINE TO PRODUCE BITUMEN IMPREGNATED FIBERBOARD, THE IMPROVEMENT WHICH COMPRISES INTRODUCING NORMALLY SOLID BITUMEN IN MOLTEN CONDITION IN THE FORM OF A STREAM HAVING A FINENESS OF LESS THAN 1/2 INCH INTO A FLOWING STREAM OF AQUEOUS SLURRY MOVING AT A RATE OF AT LEAST 3 FEET PER SECOND AND CONTAINING ABOUT 1-10% BY WEIGHT FIBER AT A TEMPERATURE BELOW THE SOFTENING POINT OF SAID BITUMEN TO CAUSE SOLIDIFICATION OF THE MOLTEN BITUMEN PREDOMINANTLY IN THE FORM OF FRANGIBLE SOLIDIFIED PARTICLES ON CONTACT WITH THE FLOWING STREAM OF AQUEOUS SLURRY AND RAPIDLY REMOVEING THE FRANGIBLE SOLIDIFIED PARTICLES OF BITUMEN FROM THE ZONE OF INTRODUCTION OF THE BITUMEN BY THE FOLLOWING STREAM OF AQUEOUS SLURRY. 